In a front-wheel drive vehicle, for example, an engine loaded on a front part of the vehicle body generates torque and a differential receives and distributes the torque to right and left front wheels. In a case of a four-wheel drive vehicle, a power transfer unit (PTU) may be used in combination with a transmission including a differential, which extracts and transfer the torque in part to rear wheels.
Also in a four-wheel drive vehicle loaded with a PTU, a structure that is capable of temporarily shifting into a two-wheel drive mode may be used. In this case, one or more clutches for temporarily cutting off power transmission are inserted into any part in the powertrain system from the PTU to the rear differential. When the clutch is disconnected, the engine is freed from load for rotation of a part of the powertrain downstream relative to the clutch. This configuration works in favor of improvement in fuel economy. A clutch requires an actuator creating sufficiently great driving force for operation thereof because a thrust force to disconnect it acts on the clutch. This may, of course, cause result in an increase of PTU size. In addition, as its operation requires considerable electricity, this may cause reduction in energy efficiency. As disclosed in WO 2015/071938 A1, clutch teeth have a meshing structure at the back thereof, having a larger angle than the clutch teeth provided to secondarily create thrust force, thereby assisting the clutch to keep in mesh. This art thus enables use of a relatively compact actuator. This meshing structure, however, requires considerable play, which might undermine reliability of the clutch.